The present invention relates to a twinkle light set, and more particularly to a twinkle light set which meets Underwriters Laboratory (UL) standards for safety.
UL Standard 588 distinguishes between the flasher bulb (LAMP, FLASHING) and the twinkle bulb (LAMP, INDIVIDUAL FLASHING) as follows:
5.16 LAMP, FLASHINGxe2x80x94A series-or parallel-connected lamp that automatically cycles on and off by means of a bimetallic strip connected in series with the filament. For series-connected strings, the flashing lamp causes all lamps connected in series with it to flash. For parallel-connected strings, only the flashing lamp is intended to flash.
5.17 LAMP, INDIVIDUAL-FLASHINGxe2x80x94A series-connected lamp that automatically cycles on and off by means of a bimetallic strip connected in parallel with the filament. The cycling of the bimetallic strip causes only the individual-flashing lamp to flash by momentarily placing a short across the filament to turn the lamp on and off.
It is well-known to provide a flasher light set wherein a flasher bulb contains a thermally sensitive element which opens and closes the electrical illumination circuit through the bulb according to its xe2x80x9chotxe2x80x9d or xe2x80x9ccoldxe2x80x9d state. When the circuit containing the thermally sensitive element opens, there is no electricity supplied to any other bulb in series electrical communication therewith, so that each such series-connected bulb is temporarily extinguished until the element cools and the circuit again closes. Thus, use of even a single flasher bulb causes an entire light set or a section thereof in series communication to have its bulbs flash on and off with the flasher bulb. The appearance of a light set in which all of the bulbs or a section of the bulbs flashes on and off in unison presents an aesthetic attraction to a viewer.
However, an even more appealing aesthetic affect is produced by a twinkle light set. Instead of a flasher bulb, the twinkle light set uses a twinkle bulb. The twinkle bulb is similar to the flasher bulb in that a thermally sensitive element opens and closes the electrical illumination circuit which provides illumination of the bulb. However, whereas in the flasher light set no current passes through the bulb when the illumination circuit through the bulb is open, in the twinkle light set, each twinkle bulb has in parallel with the illumination filament a bypass or shorting circuit. The bypass circuit (when closed) presents a low resistance, whereas the illuminating circuit (when closed) presents a high resistance. As the twinkle bulb is illuminated through the illumination circuit, it heats up the normally open switch in the bypass circuit, thereby to close the switch and provide an alternative low resistance path through which the current will preferentially flow. This in turn terminates substantially all of the current passing through the high resistance illumination circuit and leads to cooling of the bulb. After a predetermined amount of cooling, the switch in the bypass circuit returns to its normally open state so that current must flow once again through the illumination circuit.
One major difference between a twinkle light set and a flasher light set is that each twinkle bulb acts independently of the other twinkle or standard bulbs in series therewith because the twinkle bulb always passes current therethrough (whether through the illumination circuit or through the bypass circuit). Thus, in a twinkle light set, a wide variety of aesthetic affects may be obtained dependent upon the placement of the twinkle bulbs. For example, a twinkle light set may consist of a plurality of substantially vertical light strings, with each bulb in a given light string being in series. A set of light strings (at least one light string being in each light string set) may contain only ordinary or standard steady-burning bulbs, while an alternate set of light strings (at least one light string being in each light string set) may contain only twinkle bulbs. The standard bulbs remain on constantly, while the twinkle bulbs twinkle on and off independently of each other, seemingly at random, as a counterpoint to provide an enhanced aesthetic appearance. Clearly any given light string(s) may include both standard and non-standard twinkle bulbs for providing a more startling aesthetic experience.
In a conventional twinkle light set typically a large or major proportion of the bulbs (at least 50% thereof) are ordinary or standard steady-burning bulbs. Thus, even if all of the illumination circuits of all of the twinkle bulbs were, through happenstance, to open at the same time, so that each of the twinkle bulbs presented only the low resistance bypass path to the current, the standard bulbs (with their high resistance illumination circuits) would dissipate the current sufficiently to ensure safety of the light set and prevent a dangerous burn-out.
However, it is known that some twinkle light set users prefer for aesthetic reasons to modify the purchased twinkle light set and convert it to an exclusively twinkle bulb light set by replacing each standard bulb of the light set with a twinkle bulb. As a result, when, by happenstance, all of the illumination circuits of all of the twinkle bulbs are open, the current passes substantially unchecked and undiminished through the low resistance bypass circuits in a decidedly unsafe manner which can lead to melting of conductors, burning of insulation, fires, and the like. While twinkle light sets are usually sold with instructions cautioning against the replacement of standard bulbs with twinkle bulbs, users do not always heed this caution.
Accordingly, recently enacted Underwriters Laboratory (UL) regulations, Section 588, requires that a series-wound twinkle light set have a minimum of fifty bulbs per circuit (to minimize the current passing through any given bulb) and that at least twenty-five of such fifty bulbs be standard steady-burning bulbs (as opposed to non-standard twinkle bulbs). This ensures that in each circuit of a series-wound twinkle light set there are an adequate number of ordinary bulbs to dissipate the current, even if by happenstance all of the twinkle bulbs are passing the current through the low resistance bypass circuits rather than the high resistance illumination circuits.
Accordingly, it is an object of the present invention to provide a twinkle light set which meets UL standards, and in particular Section 588 thereof.
Another object is to provide such a light set which precludes the user from replacing standard steady-burning bulbs with non-standard twinkle bulbs.
A further object is to provide such a light set which is simple and economical to manufacture, use and maintain.
It has now been found that the above and related objects of the present invention are obtained in a twinkle light set comprising, alternately from one end of a light set to an opposite end of a light set, at least one standard bulb socket configured and dimensioned to operatively receive a standard (e.g., steady-burning) bulb and at least one non-standard bulb socket configured and dimensioned to operatively receive a non-standard twinkle bulb. The standard and non-standard bulb sockets are configured and dimensioned to operatively receive only standard and non-standard bulbs, respectively.
In a preferred embodiment, the interior of the standard bulb socket is sized differently (preferably smaller) in at least one dimension than the interior of the non-standard bulb socket such that the standard bulb socket cannot operatively receive a non-standard bulb.
The invention also encompasses, in combination, a twinkle bulb light set, a plurality of standard (e.g. steady-burning) bulbs and a plurality of non-standard twinkle bulbs. The exterior of the base portion of each of the non-standard bulbs is sized differently (preferably greater) in at least one dimension than the exterior of the base portion of each of the standard bulbs such that the standard bulb socket cannot operatively receive a non-standard bulb. Preferably, the non-standard bulb socket defines a keyway, the non-standard bulb defines a mating key, and the standard bulb socket lacks a mating keyway, whereby a non-standard bulb will not fit in a standard bulb socket.